Make listDir and createSymlink synchronous in pub.

utils/tests/pub/descriptor/tar.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library descriptor.tar;
 
 import 'dart:io';
 import 'dart:async';
 
 import 'package:pathos/path.dart' as path;
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:scheduled_test/descriptor.dart';
 
 import '../../../pub/io.dart';
 import '../../../pub/utils.dart';
 
 /// Describes a tar file and its contents.
 class TarFileDescriptor extends DirectoryDescriptor {
   TarFileDescriptor(String name, List<Descriptor> contents)
       : super(name, contents);
 
   /// Creates the files and directories within this tar file, then archives
   /// them, compresses them, and saves the result to [parentDir].
   Future<String> create([String parent]) => schedule(() {
     if (parent == null) parent = defaultRoot;
     return withTempDir((tempDir) {
       return Future.wait(contents.map((entry) {
         return entry.create(tempDir);
       })).then((_) {
-        return listDir(tempDir, recursive: true, includeHiddenFiles: true);
-      }).then((createdContents) {
+        var createdContents = listDir(tempDir,
+            recursive: true,
+            includeHiddenFiles: true);
         return createTarGz(createdContents, baseDir: tempDir).toBytes();
       }).then((bytes) {
         var file = path.join(parent, name);
         writeBinaryFile(file, bytes);
         return file;
       });
     });
   }, 'creating tar file:\n${describe()}');
 
   /// Validates that the `.tar.gz` file at [path] contains the expected
   /// contents.
   Future validate([String parent]) {
     throw "TODO(nweiz): implement this";
   }
 
   Stream<List<int>> read() {
     return new Stream<List<int>>.fromFuture(withTempDir((tempDir) {
       return create(tempDir).then((_) =>
           readBinaryFile(path.join(tempDir, name)));
     }));
   }
 }